Method of geochemical prospecting

ABSTRACT

A METHOD OF GEOCHEMICAL PROSPECTING BY THE TAKING OF SAMPLES OF THE EARTH FORMATION AT SPACED LOCATIONS, IN AN AREA TO BE INVESTIGATED, WHICH SAMPLES ARE ANALYZED TO DETERMINE THE CONCENTRATION THEREIN OF SIGNIFICANT HYDROCARBON GAS LEAKAGE PRODUCTS FROM SUBTERRANEAN PETRILIFEROUS DEPOSITS AND THE RESULTS OF SUCH ANANYSES CORRELATED WITH SAMPLE LOCATION TO PROVIDE INFORMATION CONCERNING THE PRESENCE OF SUCH DEPOSITS IN THE AREA.   THE METHOD INCLUDES THE TAKING OF SOIL SAMPLES IN A MANNER TO OBTAIN AND PRESERVE NON-ADSORBED, PORE GASES IN THE SAMPLES AND THE USE OF SUCH GASES WITH OR WITHOUT THE ADSORBED GASES OF THE SAMPLES IN CARRYING OUT THE ANALYSES WHOSE RESULTS ARE CORRELATED WITH SAMPLE LOCATION TO OBTAIN THE DESIRED INFORMATION.

Oct. 24, 1972 L. HORVITZ 3,700,407

METHOD OF GEOCHEMICAL PROSPECTING Filed June 30, 1969 FIG] Leo Horv/tz INVE N TOR A T TURNEY United States Patent EP 5 Claims ABSTRACT OF THE DISCLOSURE A method of geochemical prospecting by the taking of samples of the earth formation at spaced locations, in an area to be investigated, which samples are analyzed to determine the concentration therein of significant hydrocarbon gas leakage products from subterranean petroliferous deposits and the results of such analyses correlatedwi'th sample location to provide information concerning the presence of such deposits in the area.

The method includes the taking of soil samples in a manner to obtain and preserve non-adsorbed, pore gases in the samples and the use of such .gases with or without the adsorbed gases of the samples in carrying out the analyses whose results'are correlated with sample location to obtain the desired information.

BACKGROUND OF THE INVENTION In carrying out geochemical exploration for subterranean petroliferous deposits, it is customary to take samples of the earth obtained by drilling or the like at convenient depths of about eight to twelve feet in regions where the earth formation is relatively loose and from just beneath the surface up to a depth of about ten feet in hard rock areas. SoiLsamples are taken in.this manner at vspaced locations in an area which is to be investigated, usually-in accordance with a predetermined plan or pattern, and are then analyzed to determine the concentration therein of significant leakage products, such as gaseous hydrocarbons, indicative of subterranean petroliferous deposits, and the results of such analyses arecorrelated with samplelocation to obtain information concerning the presence of subterranean petroliferous deposits in the area.

Some of the methods employed heretofore in carrying out geochemical prospecting by,the use ,of soil samples are, disclosed in the following listed US. patents: 2,183,964, Horvitz, Dec. 19, 1939, Method of Exploration for .Buried Deposits;v 2,198,619, .Horvitz, Apr. 30, 1940, Geochemical Exploration; 2,270,299, Horvitz, Jan. 20, 1942, Geochemical Prospecting; 2,336,176, Horvitz, Dec. 7, 1943, Geochemical Prospecting; 2,338,643, Horvitz, I an. 4, 1944, Geochemical Prespect- In the taking of soil samples for this purpose as heretofore usually carriedout, the samples are wrapped in polyethyene sacks and brought to, the laboratory where the adsorbed hydrocarbons are removed by acid and partial vacuum treatment. It has been found, however, that while most .of .the hydrocarbons in such samples are adsorbed, considerable amounts are present in a free state in the pore space of the samples.

Attempts have been made heretofore to obtain hydrocarbon gases directly from the soil, for geochemical prospecting purposes, by drilling holes to depths of five or six feet, sealing the holes at the top and removing soil air therefrom byv pumping. Such methods have not, however, met with general'acceptance since only very small amounts of hydrocarbons significant to the presence of subterranean petroliferous deposits could be obtained in this manner, possiblydue to dilution by atmospheric air during the pumping. Moreover, the recovery of soil gases in appreciable quantities in wet areas by this method would be difficult, if not impossible.

In the carrying out of geochemical prospecting as heretofore commonly practiced, the samples are usually placed in containers or wrapped in plastic bags for transportation to the laboratory where the samples are treated, as by heating with acids or other suitable reagents in a partial vacuum, to release the adsorbed gases, no effort being made to preserve the non-adsorbed or pore gases of the sample, which may escape and are largely lost to the atmosphere. The recovery and analysis of the adsorbed gases of the samples is a relatively slow process which could in many instances be eliminated by the preservation and utilization of the non-adsorbed or pore gases ofthe samples alone, thus greatly simplifying and facilitating the prospecting of areas by geochemical methods.

SUMMARY OF THE INVENTION Briefly stated, the method of the invention comprises the taking of samples of the earth formation at spaced locations and at a convenient depth in an area to be investigated, which samples are analyzed to determine the concentration therein of significant leakage products from subterranean petroliferous deposits and the results of such analyses correlated with sample location to provide information concerning the presence of such subterranean petroliferous deposits in the area.

The method includes the placing of the soil samples in containers with water to displace non-adsorbed pore gases from the soil which are trapped above the water in the container by inverting the container. Samples of the soil in its naturally occurring condition may also be taken for use in determining the concentration of adsorbed leakage products therein.

The sample containers may be provided 'with means, such as an outlet tube having a valve or stop-cock therein, by which a portion of the gas may be withdrawn from the container, or the container may take the form of a glass jar having a screw cap, which may be opened beneath the water in an inverted position to allow the withdrawal of the gas in a well known manner by the use of a bent tube inserted into the jar into the space above the water therein.

The non-adsorbed gases thus obtained are analyzed by well known methods, such as by flame chromatography, to determine the concentration therein of significant leakage products and the results of such analyses may be used alone by correlation with sample location to furnish the desired information concerning subterranean petroliferous deposits.

The dry soil samples may also be similarly analyzed, in a well known manner, to determine the concentration therein of adsorbed leakage products, and the results of such analyses used alone or in conjunction with the results of the analyses for non-adsorbed products to give additional information concerning subterranean petroliferous deposits.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS FIG. 1 is a side elevational view illustrating one type of sample container used in carrying out the method of the invention and showing apparatus by which a sample of gas is withdrawn from the same; and

FIG. 2 is a side elevational view of a somewhat different .type of sample container which may be used in carrying out the method.

DETAILED DESCRIPTION OF A PARTICULAR MODE OF CARRYING OUT THE INVENTION In carrying out the method of the invention, samples of the earth formation at spaced locations in an area to be investigated are taken in any convenient manner, as by drilling to a desired depth. The samples thus obtained are immediately placed in containers with water which are closed and shaken to cause the material to mix thoroughly with the Water to release gases in the interstices of the samples by displacement, and the containers may then be inverted to trap the gases in the containers above the water.

Any suitable type of container may be used for the purpose of collecting the samples, such as glass jars provided with screw caps which may be tightly sealed. The jars may be partly filled with distilled water before taking the samples, and the jars may be graduated to indicate the quantity of sample introduced by the amount of water displaced thereby.

The jars may be provided with outlet tubes having stop cocks by which the gases may be withdrawn in a usual manner for testing, or the gases may be removed by other convenient means.

Under some conditions, sodium chloride or other material may be dissolved in the water used in the containers to reduce the solution of the gases therein.

In taking samples in this way, the soil is introduced into the containers as quickly as possible after removal from the ground to prevent undue loss of gas to the air.

For purposes of comparison and to determine the presence and amount of adsorbed gases in the soil, soil samples in the naturally occurring condition may also be taken in the usual way as by wrapping the same in plastic bags for removal to the laboratory.

The samples are preferably transported to the laboratory for analysis, where portions of the gases above the water may be removed by withdrawing the same through the outlet tubes, or if the containers are not provided with outlet tubes, the jars may be opened in an inverted position under water and a portion of the gases removed in the usual way by introducing a bent glass tube upwardly into the space above the water through which gases may be withdrawn.

A suitable type of container for the collection and preservation of soil samples in accordance with the method of the invention, and apparatus for removing a gas sample therefrom, is illustrated in FIG. 1 wherein the container takes the form of a glass jar, or the like, having a threaded neck 12 and which is provided with a screw cap 14 for closing the same. Suitable means, such as a rubber seal ring 16 of a well known type may be provided to form a fluid tight seal between the cap and jar when the cap is screwed in place. The jar may, if desired, be graduated in the usual manner, as seen at 18.

The jar may be conveniently filled to a predetermined level with distilled water, and in taking a sample, the same is placed into the jar which is then closed, shaken, and inverted to trap any gases displaced from the sample above the water in the jar.

Portions of the gases may conveniently be removed from the jar by opening the same in an inverted position with the neck 12 extending beneath the water in a tank or pneumatic trough 20, and inserting one end of a bent glass tube 22 upwardly to a point above the level of the water in the jar, and through which the gas may be withdrawn in a well known manner.

A somewhat different type of sample container is illustrated in FIG. 2, wherein the jar 10' has a threaded neck 12' and a screw cap 14' for closing the same, which is provided with an outlet tube 24 having a valve or stop cock. With this form of sample container, the sample is collected by placing the soil in water in the container, which may then be closed, shaken and inverted to trap the pore gas above the water. To remove a portion of the gas, any suitable apparatus for that purpose may be connected to the outer end of the tube 24 with the container in an upright position and the stop cock 26 opened to allow the Withdrawal of the gas, after which the stop 4 cock may be closed to retain the remaining gas in the container.

In the collection of samples by this method, it has been found that, in general, approximately twenty-five percent of the pore gases are retained in a dissolved condition in the water, while seventy-five percent of the gases are trapped above the water. The actual proportion of the gases retained by the water may, of course, be determined by analysis, and it will be apparent that the amount so retained will vary somewhat dependent upon the temperature.

The gas samples obtained in this manner are analyzed in a well known manner, as by chromatographic methods, to determine the concentration therein of significant hydrocarbon leakage products, such as methane and ethane and heavier hydrocarbons, and the results of such analyses are then correlated with sample location to provide information concerning the presence of subterranean petroliferous deposits in the area under investigation.

By taking the soil samples by placing the same in containers with water, as described above, the results of the analyses may be readily expressed in parts by volume, when it is desired to expedite the work of correlating the results with sample location.

Where great accuracy is desired, the soil samples are also similarly analyzed by heating the same with acids to release adsorbed gases from which carbon dioxide is removed and the remaining gases further purified by washing with sulfuric acid or other suitable reagents. The concentration of the significant hydrocarbon leakage products thus obtained is then determined and added to the results of the analysis of the non-adsorbed or pore gases of the samples taken with water and totals are then correlated with sample locations.

When combining the results of the analyses of samples placed in water with the results of the analyses of the soil samples seperately taken, the results of all such analyses are reduced to parts per billion by weight before correlating the results with sample location.

By the use of chromatographic methods of analysis, the concentration of significant hydrocarbon leakage products can readily be determined within a few parts per billion of the sample, and by the method of the present invention, making use of the non-adsorbed gases of the samples, obtained as described above, the geochemical prospecting of an area may be greatly facilitated.

What is claimed is:

1. The method of geochemical prospecting for subterranean petroliferous deposits which comprises:

taking a soil sample of the earth formation at each of spaced locations in an area on the surface of the earth to be investigated,

enclosing each sample of said earth formation in a separate container with water to allow separation in the container of unadsorbed or pore gases from the sample, and

removing a portion of the unadsorbed gases so separated and analyzing the same to determine the concentration therein of significant leakage products whereby the analysis will be indicative of subterranean petroliferous deposits.

2. The method of geochemical prospecting as claimed in claim 1 wherein each sample of said earth formation is taken at a depth no greater than about 12 feet.

3. The method of geochemical prospecting for subterranean petroliferous deposits which comprises:

taking a soil sample of the earth formation at each of spaced locations in an area on the surface of the earth to be investigated,

enclosing a portion of said sample of said earth formation in a receptacle in the condition in which it was removed from such location,

enclosing another portion of said sample in a container with water and closing the container to allow separation of unadsorbed or pore gases therefrom and to trap such gases above the water in said container,

removing a portion of said unadsorbed gases from above the water in each container and analyzing the same to determine the concentration therein of significant leakage products, and

analyzing the first mentioned portion of each sample to determine the concentration therein of such leakage products thereby the combining of the analysis will be indicative of subterranean petroliferous deposits.

4. The method of geochemical prospecting as claimed in claim 3 including heating the first mentioned portion of said sample with acids to release adsorbed gases before analyzing for significant hydrocarbon leakage products.

5. The method of geochemical prospecting as claimed in claim 2 wherein each sample of said earth formation is taken at a depth no greater than about 12 feet.

References Cited UNITED STATES PATENTS 2,370,793 3/1945 Horvitz 23-230 EX 2,374,227 4/1945 Metcalf 23-230 EX 2,212,681 8/1940 Dunn 23-230 EP OTHER REFERENCES Mills, B.: The Oil Weekly, Aug. 1, 1938, pp. 18-20.

MORRIS 0. WOLK, Primary Examiner 15 R. M. REESE, Assistant Examiner 

